A digital-to-analog converter (DAC) converts a digital signal into an analog signal. This conversion, however, introduces some amount of conversion noise into frequencies other than that of the digital signal. The level of noise emitted in any given out-of-band frequency affects the quality of signals occupying that frequency, at least to the extent the noise level exceeds a specified tolerance for noise.
Conventional or Nyquist-rate DACs, while having relatively low sampling rates and power consumption, do little by themselves to suppress the level of noise introduced into a given out-of-band frequency. Although increasing the DACs' resolution generally lowers the level of noise introduced, analog design complexity and chip area restrictions limit the amount by which the noise level can be lowered.
Without the same design complexity and area restrictions, noise shaping DACs significantly decrease the level of noise introduced within a certain bandwidth by moving noise from lower to higher frequencies. However, noise shaping DACs require oversampling of the digital signal, and, thus, may consume more power than a conventional DAC. This oversampling also limits the frequencies at which noise shaping DACs can effectively decrease noise levels.
Accordingly, none of the above-described conversion approaches are entirely advantageous under all circumstances and for all out-of-band frequencies.